Various resin compositions have conventionally been used as matrices for composite materials. In the particular field of thermosetting resins, epoxy resins have widely been used as matrix resins because of their excellent mechanical properties, such as strength, elongation, heat resistance, etc., but when reinforcing materials are used composite materials containing reinforcing materials become more or less strengthened and, generally, the strength of reinforcing material is reflected in or transferred to the composite material. However, even in the case of using epoxy resins, the degree of strengthening or transfer due to the reinforcing materials is still unsatisfactory particularly in terms of compression characteristics and, therefore, improvement in this respect has been demanded. An attempt to this effect was directed to an increase in rigidity of resins per se, but generally an increase in rigidity is accompanied with an unfavorable increase in heat resistance, resulting in a significant reduction in elongation. Such resins cannot be used in some applications because of their brittleness. It was proposed in The British Polymer Journal, 15, 66 (March, 1983) that a reaction product between an epoxy compound ##STR1## and an amide compound ##STR2## is added to a system comprising an epoxy resin and a hardener to thereby improve the physical properties of resins, but no consideration is given to the improvement of the compression characteristics of the composites when they are used as a matrix resin for composite materials. In connection to the above proposal, there have also been proposed a reaction product between an epoxy compound and an amine compound in EP-A-103392 and a reaction product between an epoxy compound and an amide compound in EP-A-103968, but neither contains any suggestion of these materials for use as a matrix resin for composite materials.